The subject matter of the present invention relates generally to a method and apparatus for determining the optimum yield axis of a log and centering such optimum axis on a reference axis by means of an optical log scanner which transmits light to detectors between the side of the log and a reference edge. In particular, the invention relates to such an apparatus and method used in a veneer lathe charger for centering the log in alignment with a reference axis and transfering it from the reference axis to the veneer lathe axis by a pair of pivoted pendulum-like transfer arms. However, the present invention can also be used for other purposes such as in a sawmill for sawing the log into boards in a predetermined pattern after the maximum yield axis has been determined. In the present invention, adjustable reference edge means are provided at positions along the log spaced a predetermined distance from the reference axis. Light is transmitted through the space between the side of the log and such reference edge means to detectors which may each include a fixed linear array of photosensitive diodes that are electronically scanned to take a reading. The distance between such reference edge means and the surface of the log is measured by the optical scanner at different angles of rotation of the log and such distance signals are fed to an electronic computer to determine the optimum yield axis of the log.
Previously, the optimum yield axis of a log has been measured by using transmitted light optical scanners, as shown in U.S. Pat. No. 3,736,968 of H. G. Mason et al, granted June 5, 1973, U.S. Pat. No. b 3,746,065 of H. G. Mason, granted July 17, 1973 and in U.S. Pat. No. 3,902,539 of O. Ketteler, granted Sept. 2, 1975. However, unlike the present invention none of these patents discloses the idea of transmitting light between a reference edge means and the side of the log to measure the distance from such reference edge to the log surface. In addition, there is no indication that the log should be rotated during scanning for determining its optimum yield axis and the log repositioned by moving the scanning spindles vertically and horizontally in response to a control signal produced by the scanner to align the optimum axis of the log with the reference axis in the manner of the present invention. Further, there is no disclosure of using pivoted pendulum-type transfer arms to engage the ends of the log axis after the log has been repositioned, reclamped and the spindles removed, for transferring the log from the reference axis to a veneer lathe in the manner of the present invention.
It is indicated in U.S. Pat. No. 3,852,579 of F. Sohn et al, granted Dec. 3, 1974, that it is desirable to reposition the spindles of a lathe charger after the optimum axis of the log is determined by an optical scanner during continuous rotation of the log. However, unlike the present invention this prior apparatus employs a light reflection scanner, rather than a light transmission scanner, which detects light reflected from the surface of the log. In addition, this prior apparatus does not employ a reference edge means along the side of the log together with a light transmission scanner in order to measure the distance between the log and such reference edge means which is spaced a predetermined amount from the reference axis in the manner of the present invention. In addition, there is no use of pivoted pendulum-type transfer arms for engaging the ends of the log and moving it from the reference axis to the veneer lathe axis. Finally there is no clamping means for reclamping the log after it is repositioned at the reference axis and holding such log while the scanning spindles are removed and the transfer arms engage the log in the manner of the present invention.
It is known from U.S. Pat. No. 3,392,765 of B. B. Brookhyser et al, granted July 16, 1968, to provide a veneer lathe charger with a log lowering device and a releasable clamping means formed by three clamp arms. However, this patent does not disclose the use of any type of optical scanning after clamping, much less light transmission scanning with a reference edge means, for determining the optimum yield axis of the log and repositioning the optimum axis of the log in alignment with a reference axis. Neither does it show the use of pivoted pendulum-type transfer arms for transfering the log from the reference axis to the veneer lathe axis. U.S. Pat. No. 3,787,700 of L. H. Chasson, granted Jan. 22, 1974, does show it is old to use a linear area of photosensitive diodes as a detector in an optical scanner for measuring the diameters of logs. However, it is not employed in a light transmission optical scanner with a reference edge means.
The log centering apparatus of the present invention has many advantages over those shown in the above-described patents including a simpler and more accurate optimum yield axis measurement apparatus using a light transmission optical scanner and linear diode array detector of faster readout time with a reference edge means which is not sensitive to detector movement due to machine vibration, etc. Furthermore, the present lathe charger apparatus provides a completely automatic apparatus for determining the optimum yield axis of the log, repositioning the log to move such optimum axis into alignment with a reference axis and transferring the log from such reference axis to the veneer lathe axis.